Building automation systems (BAS) are used to coordinate, manage, and automate control of diverse environmental, physical, and electrical building subsystems, particularly HVAC and climate control but also including security, lighting, power, and the like. Typical existing BAS systems are hardwired or use a proprietary communication standard or protocol to link the various subsystems and provide system-wide user access, monitoring, and control. A BAS may comprise a plurality of end devices, a communication network, a server engine, and a graphical user interface (GUI) or other means of providing control and reporting data to a user. The end devices are each typically associated with a room, a space, a system, or a subsystem for at least a portion of a building or a campus. The server engine may be a wide variety of computer processor based control systems that may comprise a processor, a computer readable storage mechanism, and a user-interface. The communication network may support a plurality of communication protocols and communicatively couples end devices to the server engine.
The introduction of BACnet™, an ASHRAE (American Society of Heating, Refrigerating and Air-Conditioning Engineers) and ANSI (American National Standards Institute) protocol standard some uniformity of network communications has been achieved in the industry. BACnet™ was intended to standardize HVAC interoperability and serve as a solution to industry-wide issues. In use, however, BACnet™ exists in multiple versions and includes various non-standard feature functions. Current BACnet™ standards include ANSI/ASHRAE Standard 135-1995, ANSI/ASHRAE Standard 135.1-2003, ANSI/ASHRAE Standard 135-2004, ANSI/ASHRAE Standard 135.1-2007, and BACnet-2008. Therefore even with the use of a standard network protocol such as BACnet™ the communication capabilities of various end devices may not always be determinable.
Examples of the types of data that these systems collect about the space, building or system they are may include pressures, temperatures, humidity level, power/energy readings, and other run-time statistics. Often it is desirable to periodically gather these measurements in order to establish trends and adapt to changing conditions. The period of time over which this data is gathered may also depend on a variety of factors such as the nature of the data, the preferences of the user, and the quantity or nature of data to be gathered.
In the situation where multiple measurements of these values must be made in a complex system the amount of data gathered may quickly become very large and exceed the capability of the system to collect all of the desired data in a given timeframe. The communication speed of the network connecting the various components of the system will also be a factor in the amount of time required to collect the data. Other unpredictable factors such as equipment failure, power outages, or communication network interruptions may also impact the ability of a BAS to collect the desired data.
For example, the amount of pressure in a steam pipe providing heat to a building may need to be gathered once every minute, the temperatures of the various rooms in that building may only need to be gathered once every five minutes, the power/energy readings for the building may need to be harvested once every fifteen minutes, and the other run-time accumulations of data may be gathered once every hour. If four types of data are to be gathered at the beginning of the hour the amount of data take more than one-minute to collect the system may be unable to commence the collection of the pressure reading at the beginning of the next 1-minute interval. One potential solution to efficiently gather all of the data may be to increase the speed and bandwidth capability of a BAS communication network. However, this is not always a viable option due to the presence of legacy equipment that cannot communicate at higher rates or the costs associated with installing an upgraded network may be prohibitive.
Similarly, it may be cost effective in certain circumstances to upgrade a low cost item such as a sensor, thermostat, or smoke detector with a more advanced model capable of faster communication rates but the same logic does not necessarily apply to larger and more expensive items such as furnaces, chillers, or clean-room equipment. A large volume of low cost end devices may also create a financial hurdle to system wide upgrades when the environmental controls for a large building, office complex, or campus are considered for an upgrade with the goal of improved data collection performance. Therefore, a need exists for a system and method of periodically harvesting data from a plurality of devices, equipment, sensors, or locations, where the periodic data harvesting has characteristics that would cause an over-run condition when the amount of data to be harvested multiplied by the time it takes to harvest the data exceeds the capacity of a system.